We have perfused the isolated-ventilated rat lung with perfusates containing substrates for lipid metabolism. We are testing the role of lipoprotein lipase in the lung in the hydrolysis of triglycerides. At present we are perfusing with emulsions of triglycerides with differences in hydrolysis of these triglycerides by the rat lung and the rate of incorporation of fatty acids also varies. We are now studying the fate of partial glycerides in the rat lung.